Sunday, June 28, 2009

Anthropomorphising the virus - Prof Tambyah's view

NUS' Prof Paul Ananth Tambyah's opinion piece in the Sunday Times today, about H1N1, entitled 'Understanding the 'mind' of a virus' provided an interesting and useful insight into evolutionary virology. He makes some interesting points - such as that among other things, if you want to be a successful virus you should try and avoid the host immune system, and not do silly things like killing off your food supply. By his reasoning through this anthropomorphising of the virus, he reckons this virus will not turn lethal.

It is an interesting model. But he is wrong.

This novel H1N1 should not be considered an separate entity from the other H1N1 viruses,or indeed the othe Influenza A viruses. It is more correct to view the entire family of like viruses as an entity - much like the cybernetic borgs in Star Trek. These viruses seek to propagate themselves, find a utilizable biological niche to occupy and as Prof Paul Ananth points, need to stay ahead of host immune systems by a constant changing of their disguise. If they remain genetically static,develop either useless non-infective characteristics, or virulent ones which may overdo their virulence and kill off the host. These are random events. There is a balance that a successful virus strain strikes, but it cannot keep that position indefinitely because the host immune system will eventually hunt it down, and destroy it.

The common cold and Infuenza A have been extremely successful in this constant change and adaptation and engaging us poor humans in this biological cat and mouse game. And they will remain very successful. Influenza A will from time to time produce a virulent and lethal strain. Statistics don't lie. It's only a matter of time. This strain may arise in the most unexpected of places; as this one did. And as we will not have the immunity for it, many will die. But the survivors of the the onslaught will live to fight another day. And they will be stronger. Until the next real pandemic arrives. And so on.

7 comments:

Paul Ananth
said...

Thanks very much for your comment...

I beg to differ...

Viruses that are well adapted to their hosts tend not to be lethal. In fact, the excess mortality associated with the previous influenza pandemics was not really that high with the notable exception of 1918. That was an unusual situation complicated by the trenches of Flanders and the high rate of bacterial secondary infections..

As you correctly point out, the common cold is one of the best human adapted viruses. There are hundreds of strains of rhinoviruses and no long lasting immunity. That goes hand in hand with the relatively benign nature of most colds...

For a novel lethal virus, I think it would have to be a relatively recent entrant onto the human scene - a zoonosis like Nipah or SARS...

Would be interested to hear the views of others including clinicians, virologists and evolutionary biologists!

Actually we don't really disagree. Just only perhaps from the point of view of whether the novel H1N1 is really a separate entity or not. To me it is just a different strain of the same Influenza A virus which has a strategy of infection and spread. Much like a large multinational pharmaceutical company having to innovate and adapt to changing needs of the market place, go through various mergers and acquisitions to compete and survive. Each new 'product' is a variant which can 'succeed' or 'fail'. It is the collect aggregate of successes and failures that eventually matters.

The common cold is really the same. And even as we agree on it's 'success' we should see it is really the same process happening because it seeds new strains very frequently. Each time a novel one emerges, it induces an immune response that eventually kills it. But overall the viral family 'succeeds'. Same except the mortality is less.

Another thing to consider is that our idea of success is very anthropocentric. We view it as successful only from the point of view of the viruses coexistence with us. This is not necessarily essential since the H1N1 for example can use pigs and birds as alternatives. In any case, even if we consider the worst pandemic, the 1918 one, even at a case-fatality rate of 10-20%, that's not bad stats for a virus. I mean, you get global spread for knocking off only 10-20% of your food source? Not bad at all.

From an evolutionary biology point of view, I am not sure if the question of whether the H1N1 is a separate “entity” makes sense (am not sure what “entity” means in virology) because in evolution, there are no real clear-cut boundaries. But I tend to support Gigamole’s views that one should really see the current virus as part of a large population of viruses that have mutated. Populational thinking is really the correct way of thinking in evolutionary biology (not entities or species, which are arguably human abstractions of nature).

The less biologically-inclined readers (or even medical doctors) may be interested to know that this phenomenon of parasites and hosts is really more general thing (and many of them have lethal endings). There are parasites (toxoplasma) that infect rodents to make them less fearful of cats (!), parasites (a wasp larva) that infect spiders to build special webs that the parasites like (!!), and even ants who are parasites that enslave other ants for example as a “car” by sitting on it and steering its antennae (!!!).

Just a curious question: how widely known among the medical fraternity is the book by Neese & Williams called Why we get sick? I’m sort of interested in the extent of penetration of evolutionary thinking among local doctors.

The MOH website s pretty good and is updated end of everyday.http://www.moh.gov.sg/mohcorp/pressreleases.aspx?id=22370

In any case, the numbers now don't mean very much because we are moving into the phase where cases become very much unreported. Flu cases are not sent for diagnosis. Often a presumptive diagnosis is made but most feel no point going through the hassle of reporting. Even if a proper diagnosis is made, Tamiflu is only used for 'at risk' individuals. If you are young and healthy, nobody bothers too much.

FA: "Just a curious question: how widely known among the medical fraternity is the book by Neese & Williams called Why we get sick? I’m sort of interested in the extent of penetration of evolutionary thinking among local doctors."

I don't think it does to any significant degree. The great failure of our medical curriculum is that it tries to make young kids into doctors (now more so into 'clinician-scientists) without making them first a life scientist/human biologist. Biology isn't even a prerequisite anymore to enter medical school.

I haven't read Neese & Williams. Would it be a reading you would recommend?